This invention relates to an automatic weighing apparatus and method wherein the weight of a batch of articles and the volume occupied by the articles within a package can be held within preset allowable limits.
Some articles, such as cornflakes and potato chips, experience widely different degrees of swelling because of such processing conditions as applied temperature and material mixture. Such articles therefore differ in shape and size and vary greatly in apparent specific gravity. They also tend to crumble. When weighing out these articles and then packaging them, there are instances where the volume of the packaged product is too large or too small, even though the weight of the articles in the bag or package is equal to a target value or closest to the target value within preset limits. In other words, the change in volume of the packaged articles is in inverse proportion to the change in apparent specific gravity. Since the capacity of a package receiving the articles generally is fixed, too small a product volume in comparison with the package size gives the consumer the impression of a weight shortage. On the other hand, too large a product volume can lead to an improper seal because the package will be too full, and can cause the articles to overflow from the package and impair the packaging process. Accordingly, it is required that volume as well as weight be held within preset allowable limits.
In an effort to satisfy the foregoing requirement, an arrangement has been proposed in which the weighing apparatus is provided with a specific gravity sensor and crusher. The weight of a batch of articles and the volume thereof are held within preset allowable limits by actuating the crusher when a low specific gravity is sensed, and increasing the weighed out value when a high specific gravity is sensed. However, this proposed method damages the articles unnecessarily and destroys their original shape. It also gives rise to extremely small fragments which attach themselves to the weighing hoppers of the weighing apparatus, thereby producing a weighing error. These fragments may also pile up upon a vibratory conveyor, thereby promoting an irregularity in density during the weighing operation. In addition, these fragments and the finely crushed articles produced by the crusher tend to separate from articles which have not been crushed, and one cannot tell when these finer fragments will form a single mass and then be discharged from the apparatus. Accordingly, there is no assurance that raising the weighed out value will necessarily result in a larger volume.